Question

could a complex (undefined) medium be used for a citrate test? why or why not?

Answer 1

Yes it can be used a complex medium for citrate test . Organisms growing in undefined agar are capable of using citrate as the sole carbon source and they can metabolize the ammonium salt in the medium (serving as a sole nitrogen source for growth.

Use of citrate results in the creation of carbonates and bicarbonates as byproducts. Organisms degrading citrate must also use the ammonium salts, producing ammonia,thus increasing the pH of the medium.The increase in pH then causes color change in the bromothymol blue indicator, turning it blue. Under neutral conditions the medium remains a green color. The color change to blue is useful because growth on citrate agar is often limited and would be hard to observe if it were not for the color change.